I agree with Ard, but also there's more weight to the entire outfit. It's like going from a light 6 ft spinning out fit you might use for trout to a 10 ft surf rod. The rod, the reel & the line weighs more.

Weight requires more energy to handle, and usually means the casting stroke has to be adjusted. It's the same cast as Ard said, but you'll be waving around a considerable difference in actual weight.

I know when I use my 3 or 4 wt a lot then go to using my 9 or 10 wt, I feel the difference & have to adjust.

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